Process for the purification of waste water

ABSTRACT

Removal of impurities from waste waters resulting from the manufacture of phenol/formaldehyde resins. Add at least one phenol to waste water, in quantity sufficient to bring phenol: formaldehyde molar ratio to from 1:1.02 to 1:1.12; adjust normality to from 0.015 to 0.10 N; heat for prolonged time at 80*-85* C., thus evaporating lower-boiling solvents; evaporate water at temperatures between 5* below boiling point of solution and 116* C.; recover liquid resin substantially free of resite, using finely divided air to aid evaporation of remaining solvents, if desired. Suitable apparatus includes a mixing tank with lines to feed it with contaminated water, acid, and phenol. The tank discharges to a heatable reservoir which has a gravity drain to a settling tank as well as an off-take for gaseous products and a bleed-off line from an intermediate zone for conveying fluids to an overflow tank. That tank has a return line to the reservoir and a gravity drain for liquid resin. It is connected also to an expansion boiler which is heated by fluid from heat exchange units. A stack removes vapor upwardly and a gravity drain conducts liquid resin downwardly to a storage vessel. A bleed-off line from an intermediate zone in the last mentioned drain to an acid recovery vessel may be added, if desired. Air injectors are installed as needed to maintain circulation.

United States Patent Adegeest [15] 3,655,047 51 Apr. 11, 1972 [54]PROCESS FOR THE PURIFICATION OF WASTE WATER Marco Adegeest, Zandvoort,Netherlands [73] Assignee: Corodex, N.V., Zandvoort, Netherlands [22]Filed: Nov. 6, 1970 [21] Appl. No.: 87,557

[72] Inventor:

Primary Examiner-Michael Rogers Attorney-Synnestvedt & Lechner 5 7]ABSTRACT Removal of impurities from waste waters resulting from themanufacture of phenol/formaldehyde resins. Add at least one phenol towaste water, in quantity sufficient to bring phenokformaldehyde molarratio to from 1:1.02 to 1:1.12; ad-

just normality to from 0.015 to 0.10 N; heat for prolonged time at 8085C., thus evaporating lower-boiling solvents; evaporate water attemperatures between 5 below boiling point of solution and 1 16 C.;recover liquid resin substantially free of resite, using finely dividedair to aid evaporation of remaining solvents, if desired. Suitableapparatus includes a mixing tank with lines to feed it with contaminatedwater, acid, and phenol. The tank discharges to a heatable reservoirwhich has a gravity drain to a settling tank as well as an offtake forgaseous products and a bleed-off line from an intermediate zone forconveying fluids to an overflow tank. That tank has a return line to thereservoir and a gravity drain for liquid resin. It is connected also toan expansion boiler which is heated by fluid from heat exchange units. Astack removes vapor upwardly and a gravity drain conducts liquid resindownwardly to a storage vessel. A bleed-off line from an intermediatezone in the last mentioned drain to an acid recovery vessel may beadded, if desired. Air injectors are installed as needed to maintaincirculation.

7 Claims, 1 Drawing Figure PATENTEDAPR 1 1 I972 -INVENTOR MFIRCOHoeseesr BY SWM fwd/ ATTORNEYS PROCESS FOR THE PURIFICATION OF WASTEWATER The invention relates to a process and an apparatus for thepurification of waste water in which one or more phenols andformaldehyde have been dissolved. The invention relates in particular tothe purification of waste water produced in the preparation ofphenol/formaldehyde resins.

Several prior proposals have been made for processes for the removal ofphenols from waste water. in Kirk-Othmers Encyclopedia of ChemicalTechnology, volume 9, page 752, there has been described a process, forinstance, which deals with the removal of complex phenolic impuritiesfrom water by means of ozone.

in Dutch Pat. No. 41,215 there has been described a process in which thephenols are removed by an extraction with trialkyl or triarylphosphates.

1n Dutch Pat. Nos. 50,394 and 49,032 there have been described processesin which the phenols are extracted with esters having a lower boilingpoint than said phenols and with diphenyl ether respectively.

In Dutch Pat. No. 109,068 there is described a process for theextraction of phenols from an aqueous solution by means of a solvent forphenols.

1n Dutch Pat. No. 103,061 a process is described, whereby a solution ofaqueous phenols is first extracted with cumene and then is precipitatedwith sodium hydroxide, as a result of which sodium phenolate isobtained.

Dutch Pat. No. 92,678 relates to a process in which waste watercontaining phenol is first treated with chlorine, as a result of whichchlorophenols are obtained, and then extracted.

All these processes, however, relate to the removal of phenol only,whereas, when preparing phenol/formaldehyde resins, the waste waterobtained contains phenols and also formaldehyde, and consists partly ofa) water that is formed during the condensation step, b) theformaldehyde solution, c) the phenol, and d) the catalyst diluent. Torecover the phenols and the formaldehyde, the water has to be removed bydecanting, for instance, or by evaporating under reduced or normalpressure and re-condensing by means of a condenser.

1f the waste water should be simply evaporated by heating the bottom andwalls of a vessel, an unusable resin would be formed, which rapidlyreaches the C-stage or resite phase, i.e., becomes an infusible andinsoluble resin. In order to avoid this, and to develop a process thatis both acceptable and economical, it is necessary for the waste waterto be purified in such a way that the phenols and the formaldehyde areseparated off by converting said products into low molecular resins,while the water is evaporated.

It has been found that waste water in which one or more phenols andformaldehyde have been dissolved may be purified by adding phenol(s)thereto in such quantities that the phenolzformaldehyde molar ratio willbecome from 1:1.02 to 1:1.12, and by adjusting the normality of thetotal acid to from 0.015 to 0.10 N; heating the solution at atemperature of 80 to 85 C., and subsequently removing the water byheating at a temperature that is at or above C. below the boiling pointof the liquid mixture.

The composition of the waste water is determined by the type of resinthat was prepared. It will generally vary between the following limits:

3-7% by weight of phenols (normally :4%)

5-8% by weight of formaldehyde (normally 1- 6%) 5-7% by weight ofmethanol (summer or winter formalin) and small percentages of: a) estersformed during the course of the reaction (b.p. i 40 C.), b) organicchlorides, c) methylal (b.p. 44 C.) formed during the course of thereaction, and d) formic acid. The l-lCl normality (if HCl is used as acatalyst) of waste water to be purified is $0.015.

The process according to the present invention is carried out by addingphenol to the water.

The phenolzformaldehyde molar ratio is of the greatest importance. Saidmolar ratio, in the waste water, is generally 1:4.18, i.e. thepercentage of formaldehyde is too high. By adding phenol the molar ratiois brought from 1:4.18 to from 1:1.02 to 1:1.12. The formaldehyde willnow be bound by the phenol, as a result of which a thin, liquid resinmixture will be separated off, while the formation of very large resinmolecules, i.e., a viscous resin is avoided.

Acid, preferably hydrogen chloride, is added in order to maintain thenormality of the total acid between 0.015 and 0.10 N. Under suchconditions a resin reaction is maintained that produces a non-adherentresin, so that the fouling of the apparatus is avoided.

The fluid is subsequently heated at :t -85 C. for 30 hours or severaldays, so that part of the methanol and other volatile compounds formed(in which the resin produced would readily dissolve) will escape. As aresult, the ratio of separation of resin is considerably improved. Themethanol and other volatile substances evolved may be recovered. Theseparation of resin may be accelerated by injecting very finely dividedair. Very finely divided air may be provided in this instance, byinjecting air into the liquid through acid-resistant, sintered, porousfilters.

The preliminary heating and evaporation of the volatile products iseffected as near the surface of the liquid as possible, in order toprevent any turbulence from spreading through the entire quantity ofliquid, and to give the formed resin the opportunity to settle in a zonewhich can be drained and is unheated. In this way further polymerizationof the resin is prevented and the heat zone is kept substantially freefrom resin.

When the greater part of the liquid is free from methanol and othervolatile substances, it is heated to at least 5 C. below the boilingpoint of the liquid mixture, so as to evaporate the water. Thetemperature may not be higher than 116 C., because at highertemperatures a gradual adherence of resite or C-stage resin occurs uponthe heating surfaces, thus causing the rate of heat transfer to decreasewithin a short period of time and correspondingly causing evaporation toproceed at a slower rate. The evaporating surface of the source of heathas therefore to be such that at a steam temperature of below 116 C. theliquid to be afterreacted and pre-purified will keep on boiling.

The after-reaction thus completed will yield very small resin moleculeshaving 2 to i 6 nuclei, whereby it is observed that a four-nucleimolecule, for instance, is a molecule which contains 4 phenol and 3formaldehyde units. Two-nuclei molecules, such asdiphenyldihydroxymethane (in 6 isomers) may be observed as an emulsionof extremely fine crystals.

The resin obtained according to the procedure described above may befurther processed without presenting any difficulties. It may be used,inter alia, in preparing usual Novolac resin, though in this instancethere is less formaldehyde present in the recovered resin condensationmixture than in the prior process.

The process is preferably carried out in an apparatus which isschematically shown by the annexed drawing. A is the reaction vessel inwhich the resin is prepared. I

The apparatus comprises a mixing tank 1 which is supplied through a pipe1 with waste water to be purified. Vacuum created in the tank throughvacuum line 22 draws in phenol through the suction line 8, and acid,preferably mixed with water, through the suction line 21. Appropriatevalving is supplied for closing these suction lines when the mixing tankis to be emptied by means of pressure applied through pipe 2, whichforces the water, phenol and acid through the pipe 3 to the reservoir B.5 is a gauge-glass; S and C are, respectively, steam feed and steamdischarge lines.

The reservoir B is installed at an inclination. It is equipped with aheating member 4 and it is connected at an upper point to the dischargepipe 6 for the removal of methanol vapor and other volatile compounds.Finely divided air may be forced into the tank through an air injector5a. The pipe 28 carries fluid from the lower end of the reservoir B to aresin settling tank 7, which is connected to a pressure safety valve byway of line 23, and also has a gravity drain line 25 for removing theresin which has settled out in the lower levels of the tank. In line 28,near vessel B, means may be provided to introduce finely divided airinto B. A drain 24 may be provided for removing fluid from the tank 7. Apipe 9 is connected to an upper portion of the settling tank 7 forremoving lighter material from that tank.

An air injector 27 is connected into the pipe 9, and carries the fluidfrom the tank 7 to an overflow tank 10, from which fluid may be led backto the tank B by way of the overflow line 11. Heavier constituents ofthe material in the tank 10 may flow through the line 18 into the tank13, where separated resin is collected. Lighter constituents in the tank10 are carried to an expansion boiler or evaporator by way of a lineequipped with a pressure equalizer. Q is the after-reaction unit.

Between the expansion tank 15 and the separating tank 13 there is aprimary circulating pipe 16 which interconnects these two vessels. At orabout the level indicated by the broken line 26, indicating theinterface of hot and cold zones, connections are provided from the line16 to heat exchangers 14,14, these being supplied with fluid from theline 16 by the aid of air injectors 27",27". The point at which theconnections to the heat exchangers come off is just slightly below thezone at which the hot and the lukewarm water meet in the pipe 16.Slightly above this level is connected the drain pipe 29, whichwithdraws water mixed with acid, and conveys it back to the tank fromwhich the line 21 extends. A heated discharge pipe 17 leads from the topof the expansion tank 15 for the removal of volatile compounds.

There is a gauge 19 mounted between the tank 13 and the tank 15 for thepurpose of checking on the fluid level. This gauge may be provided withan air injector 27. At the bottom of the tank 13 there is a drain 30 forthe removal and recovery of the liquid resin.

EXAMPLE 624 liters (683 kg.) of waste water, remaining after thepreparation of a phenolformaldehyde resin which had been condensed in abasic medium, was admitted to the mixing tank together with 312 liters(341 kg.) of waste water resulting from the condensation of aphenolformaldehyde resin in an acidic medium. 84 liters (90 kg.) ofwater containing acid was mixed with these waste water portions, thiswater-containing acid having been drawn through the continuous drain 29from the after-reactor of the evaporating plant. 109 kg. of phenol wasadded to this mixture.

Before the addition of phenol, the phenolzformaldehyde molar ratio was0.43 gram mol per liter to 1.8 gram mol per liter, i.e., 1:4.18. This is40.46 g. ofphenol and 54 g. offormaldehyde per liter. After the additionof phenol the phenolzformaldehyde ratio was 0.57 gram mol per liter to0.6] gram mol per liter, i.e., 111.07. This is 53.64 g. ofphenol and18.38 g. of formaldehyde per liter.

Thenormality of the total acid mounted to 0.015.

After the addition of phenol the mixture was held at a temperature of-85 C. for 48 hours. The water was subsequently removed by being heatedto boiling temperature.

There was thus obtained 200 kg. of a thin, liquid resin mixture whichwas separated off by settling.

Inasmuch as 109 kg. of phenol was added, there have thus been recovered91 kg. of resin product (i.e., 8.8 percent by weight) from the acidwaste water.

Subsequently, another 84 liters of water containing acid was obtainedfrom the continuous drain 29 from the reactionevaporation zone C. Thiswater is required for maintaining the acidity in this zone at a constantlevel, while it also serves to adjust the acidity in the mixing tank.

I claim:

1. A process for the removal of phenol from waste water in which one ormore phenols and formaldehyde have been dissolved, characterized by thesteps of adding at least one phenol to such waste water until thehenolzfonnaldehyde molar ratio 18 brought to from 111.02 0 1:1.12;adding reagents as needed to adjust the total acid normality of thewaste water to from 0.015 to 0.10 N; heating the solution for aprolonged interval at 80 to 85 C., and subsequently removing excesswater by heating the liquid mixture to a temperature between its boilingpoint and 5 C. below its boiling point.

2. A process according to claim 1, characterized in that hydrogenchloride is used to adjust the normality of the acid.

3. A process according to claim 1, characterized in that very finelydivided air is injected through the solution, so as to accelerate theremoval therefrom of water and of such vaporizable impurities present asmay be solvents for phenol/formaldehyde resins.

4. A process according to claim 1, characterized in that the heating attemperatures of from 80 to 85 C. is maintained for at least 30 hours.

5. A process according to claim 1, characterized in that excess water isremoved from the liquid mixture by bringing it into contact with asurface which is heated to at least the temperature stated, but notabove 1 16 C.

6. A process in accordance with claim 1 in which, at the end of theprolonged heating mentioned, liquid resin is removed from a lower zonein the heated solution to cool storage, volatilized constituents areremoved from an upper zone, and water containing reagents added toadjust the normality is removed to an evaporating zone where it issubjected to temperatures sufficiently high to evaporate excess water,the liquid resin remaining being removed from the heated area to coolstorage.

7. The process according to claim 6, wherein the evaporating stepincludes the recycling of water-containing fluids through heat exchangeequipment back to the evaporating phase.

UNITED STATES PATENT oFTTcE fiE'HFICATE OF CQ ECTIQN Patent No. 3 655 0:7 Dated April 11 1972 Inventor(s) Marco Adegeest It is certified thaterror eppears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the heading, below item [21], insert:

l 30] Foreign Application Priority Data November 7, l969 Netherlands69.l68'+3- Signed and sealed this 9th day of January 1973..

(SEAL) Attest:

EDWARD M. FLETCHERJR. ROBERT GOTTSCHALK Attestlng Officer Commissionerof Paten1 FORM PO-1050 (10-69) USCOMM-DC 60376-P69 U.S. GOVERNMENTPRINTING OFFICE: I989 O-366-334

2. A process according to claim 1, characterized in that hydrogenchloride is used to adjust the normality of the acid.
 3. A processaccording to claim 1, characterized in that very finely divided air isinjected through the solution, so as to accelerate the removal therefromof water and of such vaporizable impurities present as may be solventsfor phenol/formaldehyde resins.
 4. A process according to claim 1,characterized in that the heating at temperatures of from 80* to 85* C.is maintained for at least 30 hours.
 5. A process according to claim 1,characterized in that excess water is removed from the liquid mixture bybringing it into contact with a surface which is heated to at least thetemperature stated, but not above 116* C.
 6. A process in accordancewith claim 1 in which, at the end of the prolonged heating mentioned,liquid resin is removed from a lower zone in the heated solution to coolstorage, volatiliZed constituents are removed from an upper zone, andwater containing reagents added to adjust the normality is removed to anevaporating zone where it is subjected to temperatures sufficiently highto evaporate excess water, the liquid resin remaining being removed fromthe heated area to cool storage.
 7. The process according to claim 6,wherein the evaporating step includes the recycling of water-containingfluids through heat exchange equipment back to the evaporating phase.